Switchgrass to Gas?
When President Bush spoke during his State of the Union address about turning something called “switchgrass” into a future source of ethanol, thus reducing the United States’ dependence on oil, it certainly caught R. Michael Raab’s attention.
Raab is president and founder of Agrivida, a Cambridge, MA-based biotech startup that wants to add genes to plants to make it cheaper and easier to process them into ethanol. He hopes the technology his company is developing will make ethanol derived from plants, including switchgrass, a viable alternative to gasoline.
For now, the company is focusing its efforts on corn, already a source of ethanol. But standard ethanol production uses just the kernels. Ethanol manufacturers process the kernels using enzymes that break down the starch into simple sugars. The sugars are then fed into a fermentation tank, where yeast digests them and produces ethanol. But in this process the corn stalks and leaves – about half of the plant mass – are thrown away.
Using the whole plant would produce much more ethanol – but the sugars in the stalks and leaves are in the form of cellulose, which is a much more complex chain of sugar molecules. To break down cellulose into simple sugars for the yeast requires a preconditioning process that includes heat, high pressure, and acids. Today, that process is too expensive to be worthwhile – as it would also be for switchgrass, a woody grass native to North America that can grow to nine feet tall (and which now no one uses for ethanol).
Agrivida proposes to add genes to the corn plants that will produce enzymes for breaking down the cellulose. This makes it much easier to process the cellulose into sugar, reducing production costs to a point where it’s feasible to use the whole plant, Raab says. He predicts the process will be about 50 percent cheaper than current processes once it matures. And it could be adapted to switchgrass, he says.
However, enzymes that break down a corn’s structural elements could also result in weakened stalks. So Agrivida has redesigned the enzymes to remain inactive during the plant’s life. Only when they encounter the conditions of processing, such as increased temperature or pressure or a change in pH level, are the enzymes activated. (Raab won’t explain the process in detail because it’s part of a patent application.)
Clearly, there’s a great deal of potential energy to be tapped. A study at Argonne National Laboratory estimates that a gallon of ethanol produced from kernels of corn in today’s processes provides about 20,000 BTUs more energy than the energy that went into making it. The study projects that using cellulose from switchgrass would triple that net gain, to about 60,000 BTUs per gallon, mostly because little fossil fuel would be used in farming the grass. But costs need to come down to make this practical.
It was this “cellulosic” ethanol that President Bush spoke about when he proposed adding $150 million to next year’s federal budget for research into using switchgrass. Raab says switchgrass is appealing; for one thing, an acre of land can produce four times the mass of switchgrass as of corn. And switchgrass is far hardier and easier to grow than corn. “The energy balance for ethanol from switchgrass is tremendously better,” he says. “It doesn’t require all the fertilizer, all the irrigation, all the energy intensity that corn does.”
Scientists estimate that ethanol could replace about 30 percent of the demand for gasoline without affecting food production. Right now, ethanol, mixed with gasoline, accounts for only about 2 percent of fuel in U.S. cars. Switchgrass can be grown on marginal land that couldn’t support food farming. And experiments have shown that an acre of land can produce from 6 to 15 tons of switchgrass, yielding about 100 gallons of ethanol per ton.
Edenspace Systems of Dulles, VA, is also trying to genetically engineer corn and switchgrass to be better sources of ethanol. “It’s clearly an idea that has been kicking around,” says Ken Keegstra, director of the Department of Energy Plant Research Laboratory at Michigan State University, who recently became an advisor to Agrivida. “I think whoever gets it implemented in a practical way has a real winner on their hands.”
It will take time before anyone is putting switchgrass-derived gas in their car, though. So far, Agrivida has designed enzymes on the computer and grown them in bacteria, but they still have to test how the enzymes act in plants. Raab hopes to begin field trials in late 2007, in order to get approval from the U.S. Department of Agriculture to start marketing his corn in 2010. Adapting the method to switchgrass would require an additional two or three years of academic research, Raab says.
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